separation of church and state
Has little to do with this. "God" and "Religion" are not synonymous, there is no benefit to anyone in affirming the motto. The Establishment Clause (The actual constitution base of the argument -
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof."), at its base, was to stop the nation from becoming a theocracy, as the Puritans that did precede them, or from one national religion becoming recognized above others, much like the Church of England was in Britain or the Catholic church was in...well, Europe circa 500-1400 AD. Over time, there have been a number of court rulings recognizing a broader sense of the clause, considering it to be more a safeguard from religious persecution and prevention of government endorsement in addition to establishment of a church state or a national/state church. The "Wall of Separation" was not intended to stop anything remotely religious/spiritual from being a part of the government, but to stop it from
being the government and or having a direct power on such.
Ultimately, though, America really has many more concerns than the national motto at this moment and "affirming" something that already
is seems to be a bit silly and time consuming.